# Circuit Simulator - Astable Multivibrator (Oscillator)

Astable Multivibrator (Oscillator)
Circuit Description:
This circuit is an astable multivibrator, or oscillator. The two transistors are cross-coupled in such a way that the circuit switches back and forth between two states. In one state, the base of Q1 is about one diode drop above ground, allowing a base current to flow. This keeps Q1 switched on, in saturation mode, allowing a current to flow through the collector, keeping Q1's collector voltage low, and discharging C1. Q2 is switched off, because its base voltage is not high enough to switch it on.

As the collector current into Q1 charges C1, the base voltage for Q2 goes up, until it is high enough to switch on Q2, causing a current to flow through its collector, which drops the collector voltage (the current causes a voltage drop across the resistor above it). The right side of C2 has dropped, but the voltage across it hasn't changed, so this causes Q1's base voltage to drop below ground, switching it off.

Then we get the other half of the cycle, with current flowing through Q2. This continues until Q1 turns on, and then the cycle repeats.

Discussion:
10 comments Page 1 of 1.

Thaveshni said:   10 years ago
Just try building the circuit. But put an LED between each of the 330 ohm resistors and capacitor. You will see that the LEDS blink one at a time. I recommend using a 33uF capacitor in order to see each LED blink.
(6)

Niusha said:   9 years ago
In Which multivibrator we can use one transistor?

And Who we can simulate multivibrator with one transistor?
(3)

What do you mean circuit switches back and fourth between two stages?
(1)

Pranav said:   10 years ago
R1 and R2 are the voltage dividers, which stabilize the network.
(1)

Ighodaro triumphant said:   1 decade ago
Plz! I need the principle of operation for this ciruit.
(1)

Gojunpyo said:   9 years ago
Does it not produces the complete square waves?
(6)

Walks said:   10 years ago
Need to know where this circuit is applicable.
(2)

Bitrus yunusa said:   1 decade ago
What is the used of R3 and R4?
(1)